1. Field of the Disclosure
The present invention relates generally to power supplies and, more specifically, the present invention relates to power supplies that use the flyback topology.
2. Background
Switching power supplies may be used for a multitude of purposes and applications. The flyback topology is a typical choice for switching power supplies with multiple outputs because it is often the solution with the lowest cost for many applications.
In many applications, it is often desirable for a power supply to provide output voltages that are invariant when the load current from the same output and the load currents from other outputs vary over a wide range. One example of an application where such invariant output voltages are desirable is a power supply for an audio amplifier. Audio amplifiers typically require two voltage sources of equal and opposite polarities with respect to a common reference, such as for example +40 volts and −40 volts.
It is difficult for a single flyback power supply that uses conventional methods of control to provide two invariant output voltages to audio amplifiers. Conventional methods regulate one output directly, and rely on good coupling between output windings of a transformer to keep another output voltage invariant to changes in the loads. Although the conventional method is adequate in many applications, it is unsatisfactory for audio amplifiers because of the special loading associated with audio signals.
The nature of audio signals causes the two output voltages to be loaded with unequal currents. It is common for one output to deliver a large current while the other output is delivering a small current. Imperfect coupling between windings of the transformer causes the voltage at the output with small current to rise unacceptably.